Light emitting diodes (LEDs) are well-known semiconductor light emitting devices that convert electric current into light and have been used as light sources for displaying images of electronic equipment including information communication equipment, in conjunction with green GaP:N LEDs, since red LEDs using GaAsP semiconductors were commercialized in 1962.
Nitride compound semiconductors such as gallium nitride (GaN) have high thermal stability and a broad band gap ranging from 0.8 to 6.2 eV, and therefore have received a great deal of attention in fields for the development of high-power output electronic component devices including LEDs.
One of the reasons why gallium nitride (GaN) has attracted a great deal of interest is because it is possible to fabricate semiconductor layers emitting green, blue, and white light, by using GaN in combination with other elements such as indium (In), aluminum (Al), and the like.
Due to the capability to control an emission wavelength via the use of GaN, the emission wavelength may be adjusted to a desired range suited to intrinsic properties of the materials used in compliance with the characteristics of specific equipment. For example, the use of GaN makes it possible to manufacture blue LEDs which are beneficial for optical recording and white LEDs which are capable of replacing incandescent lamps.
Thus, nitride semiconductors are widely used as base materials in manufacture of blue/green laser diodes and light emitting diodes (LEDs).
Meanwhile, conventionally, liquid crystal display (LCD) devices and active matrix organic light emitting diode (AMOLED) display devices are widely used as flat panel display devices.
OLED display devices are generally classified into active matrix (AM) type OLED display devices and passive matrix (PM) type OLED display devices according to driving method. Particularly, differently from AM OLED display devices, PM OLED display devices are current-driven devices and are very sensitive to power loss of electrodes.
It is substantially difficult to implement PM display devices due to electric power loss and changes of properties of organic materials.
That is, although PM display devices have advantages such as a simple manufacturing process and low manufacturing costs, AM display devices are more commonly used due to lower brightness of the PM display devices compared to thin film transistors (TFTs). Furthermore, it is difficult to commercialize PM OLED display devices due to such high sensitivity to electric power loss.